As I stated..................well oiled offers your protection. Bluing add professional color. If you do not care about springs that no one sees, why even bother.
I deal in a LOT of springs, what with my many antique clocks and watches, and all are blued or blue colored. HT'ing brings about a lot of that color. You never see them either, but they never rust due to the oils & greases that are always there. I have yet to see a clock spring from the last 150 years that is not blue.
No bluing will not prevent rust on it's own. You need to use a very thin film of the right kind of oil. In fact, the chemicals in cold bluing (and hot/electro bluing I have used) will actually CAUSE rusting if not washed off, neutralized, and oiled.
Two surface treatments I know of that can prevent rust on their own are nitriding with disassociated ammonia (black oxide) and TIN coating (gold hard coating). Neither of which is easy to do at home!